Multiproxy archaeobotanical analyses (starch granule, phytolith and microcharcoal) of an abandoned agricultural terrace at Wagadagam on Mabuyag Island, Torres Strait, Australia, document extensive, low-intensity forms of plant management from at least 2,145-1,930 cal yr BP and intensive forms of cultivation at 1,376-1,293 cal yr BP. The agricultural activities at 1,376-1,293 cal yr BP are evidenced from terrace construction, banana (Musa cultivars) cultivation and dramatic transformations to the local palaeoenvironment. The robust evidence for the antiquity of horticulture in western Torres Strait provides an historical basis for understanding the diffusion of cultivation practices and cultivars, most likely from New Guinea. This study also provides a methodological template for the investigation of plant management, potentially including forms of cultivation that were practiced in northern Australia before European colonization.